“Zero-drift” characteristics of an optical intraocular pressure sensor is investigated as a function of membrane dissolution and hygroscopic swelling of the epoxy layer. Both effects were studied using an analytical model based on the deflection of a circular membrane. Results from the analytical model were verified with experimental results from “bulge” testing. The analytical model was used to study the “zero drift” of the sensor as a function of changes in membrane thickness and geometry of the sensor. The results show that dissolution of the membrane and swelling of the spacer layer can contribute to zero-drift over time. The results are useful in guiding design and fabrication optimization to minimize drift in intraocular pressure sensors used for long term implantation.